Layout tools for laying out the web of structural steel beams and girders are known as disclosed in the following U.S. Pat. Nos.: 1,382,721--E. W. Cunningham; 4,228,594--A. E. Shlager; 1,046,187--W. Hernlund; 1,725,476--M. J. Poppock; 1,826,807--A. J. McDanel; and 3,731,390--J. L. Sloan et al. Steel squares also are well known. Some prior art layout tools are of complicated construction and expensive. Many are difficult to use and do not substantially speed up the layout process. Use of a simple steel square to layout the web of the beam often results in inaccurate measurements due to the presence of the fillet at the intersection of the beam web and flange which prevents butting one arm of the square against the flange while maintaining flat surface contact with the web by the other arm.